1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and more particularly to a complementary bipolar transistor including NPN and PNP transistors and a method of manufacturing the same.
2. Description of the Background Art
FIGS. 8 to 12 are sectional views of a conventional complementary bipolar transistor in Various stages of production.
Referring initially to FIG. 8, ion implantation of antimony (Sb.sup.+) is performed over a major surface of a p.sup.- type semiconductor substrate 1. Heat treatment for diffusion of impurities (hereinafter referred to as "drive") and thermal oxidation are performed to form an n.sup.+ type buried layer 2 and an oxide film 3 (in FIG. 9). The oxide film 3 is selectively etched away by photolithography technique. Masked with the remaining oxide film 3, the n.sup.+ type buried layer 2 is doped with boron ions (B.sup.+) by a means of ion implantation (in FIG. 10). The drive is performed, and the oxide film 3 is entirely removed. A p.sup.+ type buried layer 4 and an n.sup.- type epitaxially growth layer 5 are formed by means of epitaxial growth (in FIG. 11).
Isolation trenches 7 and p type channel cut layers 6 are formed, and thereafter a p.sup.- type well layer 8, a p.sup.+ type collector wall layer 9, and an n.sup.+ type collector wall layer 10 are formed. Subsequently formed are a p type base 11a, an n type base 12a, an n.sup.+ type emitter layer 13, a potential extraction layer 30, a p.sup.+ type emitter layer 14, polycrystalline silicon films 15, an n.sup.+ type external base layer 12b, and a p.sup.+ type external base layer 11b. Silicide films 16, barrier metals 17, and aluminum electrodes 18 are provided, so that an NPN transistor 100 and a PNP transistor 101 are formed (in FIG. 12). The NPN transistor 100 comprises a collector electrode 19, an emitter electrode 20, and a base electrode 21. The PNP transistor 101 comprises a collector electrode 23, an emitter electrode 24, a base electrode 25, and a potential extraction electrode 22.
The conventional complementary bipolar transistor has been manufactured in this manner. FIG. 13 shows an equivalent circuit of the PNP transistor 101.
A PNP transistor 101b has an intrinsic function of the PNP transistor 101. The p.sup.- type well layer 8 and p.sup.+ type buried layer 4, the n type base 12a, and the p.sup.+ type emitter layer 14 serve as collector, base, and emitter of the PNP transistor 101b, respectively. An NPN transistor 102 is formed parasitically on a PNP transistor 101. The n type base 12a, the p.sup.- type well layer 8, and the n.sup.+ type buried layer 2 serve as emitter, base, and collector of the NPN transistor 102, respectively. A PNP transistor 103 is a parasitic transistor, wherein the p.sup.- type semiconductor substrate 1, the n.sup.+ type buried layer 2, and the p.sup.+ type buried layer 4 serve as collector, base, and emitter, respectively. A resistor R1 is composed of the p.sup.+ type collector wall layer 9 and the p.sup.+ type buried layer 4. A resistor R2 is composed of the n.sup.- type epitaxial growth layer 5 between the potential extraction electrode 22 and the n.sup.+ type buried layer 2. A resistor R3 is composed of the p.sup.- type well layer 8 between the n type base layer 12a and the p.sup.+ type buried layer 4.
For operation of the NPN transistor 101 having such an equivalent circuit, in general, a potential extraction electrode TUB is set at a maximum potential by connecting to the emitter E of the transistor 101b, as shown by the broken lines of FIG. 13, to reduce the influence of the parasitic transistors 102 and 103. When a breakdown voltage BV.sub.TCO between the potential extraction electrode TUB and the collector C of the whole transistor 101 is lower than a breakdown voltage BVCEO between the collector C and the emitter E, breakdown occurs between the electrode TUB and the collector C before breakdown occurs between the collector C and the emitter E. A required breakdown voltage cannot be attained. The conventional complementary bipolar transistor, however, includes a PN junction composed of the p.sup.+ type buried layer 4 of high impurity concentration and the n.sup.+ type buried layer 2 of high impurity concentration. There has been a problem that the breakdown voltage of the transistor 103 having this PN junction and accordingly the breakdown voltage of the whole transistor 101 are low.
The p.sup.+ type buried layer 4 is formed by the ion implantation of boron (B.sup.+) in the n.sup.+ type buried layer 2 of high impurity concentration, and hence cannot grow very thick. Another problem is that a collector resistance cannot be reduced which is the sum of the resistance R1 and the resistance R3, and a large amount of collector current flow causes decrease in amplification factor h.sub.FE.